In recent years, soft silicone hydrogel contact lenses become more and more popular because of their high oxygen permeability and comfort. “Soft” contact lenses can conform closely to the shape of the eye, so oxygen cannot easily circumvent the lens. Soft contact lenses must allow oxygen from the surrounding air (i.e., oxygen) to reach the cornea because the cornea does not receive oxygen from the blood supply like other tissue. If sufficient oxygen does not reach the cornea, corneal swelling occurs. Extended periods of oxygen deprivation cause the undesirable growth of blood vessels in the cornea. By having high oxygen permeability, a silicone hydrogel contact lens allows sufficient oxygen permeate through the contact lens to the cornea and to have minimal adverse effects on corneal health.
One of lens forming materials widely used in making silicone hydrogel contact lenses is a polydiorganosiloxane (e.g., polydimethylsiloxane) vinylic crosslinker which can provide high oxygen permeability to resultant contact lenses. But, a polydimethylsiloxane vinylic crosslinker can affect the mechanical properties, e.g., elastic modulus, of the resultant contact lenses. For example, a low molecular weight polydimethylsiloxane vinylic crosslinker (<2,000 g/mol) may provide a resultant contact lens with a relatively high elastic modulus in order to achieve a desired oxygen permeability. A relative high molecular weight polydimethylsiloxane vinylic crosslinker is typically required for achieving both the high oxygen permeability and the low elastic modulus. However, because of its hydrophobic nature, a polydimethylsiloxane vinylic crosslinker, especially one with high molecular weight, is not compatible with hydrophilic components in a lens formulation, including, e.g., N,N-dimethylacrylamide, N-vinylpyrrolidone, N-vinyl-N-methylacetamide, or an internal wetting agent. It would be difficult to obtain homogeneous lens formulations (i.e., clear lens formulations) from use of such a polydimethylsiloxane vinylic crosslinker.
It would be even more difficult to obtain a homogeneous, solventless lens formulation from use of such a polydimethylsiloxane vinylic crosslinker. Use of organic solvents in preparing silicone hydrogel contact lens can be costly and is not environmentally friendly.
Therefore, there is a need for new hydophilized polydiorganosiloxane vinylic crosslinkers suitable for preparing a solventless lens formulation that can be used to produce silicone hydrogel contact lenses with long thermal stability.
Documents, including U.S. Pat. Nos. 4,260,725, 5,034,461, 5,346,946, 5,416,132, 5,449,729, 5,486,579, 5,512,205, 5,760,100, 5,994,488, 6,858,218, 6,867,245, 7,671,156, 7,744,785, 8,129,442, 8,163,206, 8,501,833, 8,513,325, 8,524,850, 8,835,525, 8,993,651, and 9,187,601 and U.S. Pat. Appli. Pub. No. 2016/0090432 A1, disclose that various lens formulations (which are either solvent-containing or solventless formulations) comprising one or more hydrophilized polysiloxane crosslinkers can be used for making silicone hydrogel contact lenses.